Images of the World Trade Center site show patterns of materials with spectral
absorptions indicating the presence of C-H (organic) compounds.

The map of materials containing organic compounds (Figure 1a, 1b) shows no pattern
that is indicative of the distribution of debris from the WTC collapse at the
detection limit of AVIRIS. Organic compounds include any material containing
C-H chemical bonds (e.g. plastics, paints, gasoline, and many types of solvents).

Because there are literally thousands of organic compounds and our reference
materials spectral library only contains a few samples, we do not have the
capability to uniquely identify the various types of organic materials. Because
the reference spectra covering the AVIRIS spectral range is sparse, it is also
unknown if AVIRIS has the spectral resolution to uniquely separate some types
of organic compounds. Thus the organics map here does not indicate unique compounds.
But the different colors indicate different spectral classes of organics and
indicate broadly similar compositions.

The majority of the organics mapped in this area are probably related to plastics
and paints. Paper, wood, and vegetation are also organic, but the spectral
signatures of these materials occur with other known absorptions (e.g. from
lignin, cellulose, and nitrogen) and are excluded from this map. Some aged
wood, however, does have spectral features that can be confused with the other
organics here (e.g. due to decreased signatures of lignin, cellulose, and nitrogen),
and might be included in this map.

Imaging spectroscopy has not detected more than a few percent organic material
in the WTC debris. It may be possible that more organic material exists but
was not spectrally observable at the surface with AVIRIS.

Absorptions due to CH occur near 2.3 microns: the same location as (OH) absorptions
in serpentines and amphiboles (asbestiform minerals). This coincidence results
in a higher threshold detection limit for asbestiform minerals when CH-absorptions
are present in the spectrum. Fortunately, CH-compounds also have additional
absorption features (e.g. those near 1.65 to 1.75 microns, Figures 2a, b, c)
that make detecting such compounds possible and reducing false positive identifications
of asbestiform minerals. Thus, locations on this map where CH-compounds are
present also indicate locations where asbestiform minerals are indeterminate.